The present invention relates to a method for evaluating an ocular optical lens and an apparatus and a memory medium therefor and, more particularly, to a method for evaluating an ocular optical lens comprising visualizing an Abbe number of an ocular optical lens in the form of a region of comfortable vision displayed on a video screen and an apparatus and a memory medium therefor.
The desired properties for a lens material used to make spectacles include a high refractive index, a high Abbe number, a low specific gravity, excellent workability, excellent tinting performance and chemical resistance. Among these properties, the refractive index and the Abbe number are particularly important optical properties.
With respect to a spectacle lens having a great dioptric power, the higher the refractive index of the lens, the smaller the thickness required. Aesthetically, thinner lenses have better appearance and are lighter in weight. With respect to the Abbe number, the higher the Abbe number of the lens the smaller the chromatic aberration in peripheral portions of the lens, which corresponds to a greater lens area affording comfortable vision for the user.
Historically, it had been difficult to produce an ideal lens material having both a high refractive index and a high Abbe number. Typically, a spectacle lens having a higher refractive index tended to have a lower Abbe number. However, as eyeglass lens production technology progressed, materials having a high refractive index, a high Abbe number, and suited for making spectacle lenses have been developed. Spectacle lenses prepared using these new materials have excellent optical properties and are now becoming commercially available.
Generally speaking, a difference in the refractive index of a spectacle lens manifests itself as a difference in the external shape (i.e. the thickness) of the lens when spectacle lenses of the same dioptric power are compared. Therefore, differences in the refractive index between eyeglasses can be easily appreciated by a person wearing spectacles. However, a difference in the Abbe number of a spectacle lens is less apparent because the difference cannot be seen as a difference in the external shape of the glasses. Consequently, lenses having different Abbe numbers cannot be easily appreciated by a customer wishing to buy a pair of spectacles. To help the customer understand the effect of the Abbe number on the spectacle lenses several methods have evolved. For example, the Snellen""s visual mark is one technique utilizing a pattern of xe2x80x9cExe2x80x9ds for exhibiting an actual visual image based on the Abbe number used for simulating optical lens effects (i.e. visual acuity) on a retinal image. The image of actual vision produced by this technique causes the peripheral portions of the image to be blurred due to the unfocused colors of the visible spectrum. The degree of the peripheral blur depends on the Abbe number.
It is desired by optometrists and professionals who sell spectacles, or eyeglasses, that customers be able to readily appreciate how a difference in a lens""s Abbe number can correspond to a difference in actual vision because an educated consumer is a more satisfied customer. Specifically, when the customer can appreciate immediately the superior actual vision provided by spectacles made using the newer excellent lens material and having a high Abbe number, then the excellent spectacle lenses can be immediately recognized as distinguished products different from ordinary spectacle lenses.
Unfortunately, differences in the Abbe number of lenses remain difficult for a layperson to recognize. For the image of actual vision described above, blur due to slightly unfocussed colors appearing in the Snellen""s visual mark is similar to that appearing in the actual retinal image. Therefore, it is mostly professional persons skilled in the art who are able to recognize and appreciate the affect differences in the Abbe number have on an eyeglass lens. Ordinary people who will wear the spectacles may not be aware of the blurring of their peripheral visual fields.
The present invention is directed to providing a method for facilitating the evaluation of an ocular optical lens which overcomes the above problems by displaying the difference in the Abbe number of an ocular optical lens as a difference in the area of a region thereby making plain the visually recognizable difference affected by the Abbe number and an apparatus and a memory medium used therefor.
The present invention provides, in a first preferred embodiment, a method for evaluating an ocular optical lens which comprises: inputting a value of an Abbe number expressing a degree of chromatic aberration at each point on an ocular optical lens; obtaining a region of comfortable vision based on the input values, the region of comfortable vision being a region in which a specific value of visual acuity is surely obtained; and evaluating a difference in visibility due to a difference in the Abbe number of the ocular optical lens based on an area of the region of comfortable vision. The area of the region of comfortable vision may be expressed as a number or understood from an area of the region displayed on a screen. In accordance with the present embodiment, the difference in the visual acuity due to the difference in the Abbe number is recognized not as a retinal image but as the region of comfortable vision in which a specific value of visual acuity is surely obtained. Therefore, the difference in visual acuity due to the difference in the Abbe number can be directly recognized by comparing regions of comfortable vision.
In a second preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to the first preferred embodiment, wherein the region of comfortable vision is displayed as an image.
In a third preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to first and second preferred embodiments, wherein the region of comfortable vision is a region marked out with and contained in a circle, an ellipse or a closed curve.
In a fourth preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to the first three preferred embodiments, wherein a plurality of regions of comfortable vision are obtained from Abbe numbers of a plurality of ocular optical lenses based on different specifications and displayed on a single screen so that the plurality of regions can be compared. When a plurality of the regions of comfortable vision are exhibited on the same screen as overlapping images, the comparison can be made easily and the difference in the vision experienced by the lens wearer due to the difference in the Abbe number can be directly recognized.
In a fifth preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to any one of the first four embodiments, wherein the region of comfortable vision is displayed on a screen with the center of the region placed at an optical center of the ocular optical lens being evaluated, and an image in the shape of a lens frame is also displayed on the same screen.
In a sixth preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to any one of the first five embodiments, but enables simulation of a change in the region of comfortable vision resulting from altering at least one of the Abbe number, a value of visual acuity, a spherical dioptric power, a cylindrical dioptric power, an angle of cylinder axis, an additional dioptric power, and values of IN/OUT and UP/DOWN coordinates that map out a layout of a lens shape. The additional dioptric power is a datum related to a progressive multifocal lens.
In a seventh preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to the methods of the first six embodiments, wherein an image of actual vision corresponding to the region of comfortable vision is created based on the Abbe number used for obtaining the region of comfortable vision and the image of actual vision and the region of comfortable vision are displayed on the same screen so that the image and the region can be visually compared.
In an eighth preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to the methods of the first seven embodiments, wherein a Landolt""s ring or a Snellen""s visual mark is used to create the image of actual vision.
In a ninth preferred embodiment, the present invention provides a method for evaluating an ocular optical lens which comprises: arbitrarily selecting a point inside a lens shape of one ocular optical lens and, based on prism characteristics at the selected point, obtaining an equivalent visual region in which a specific value of visual acuity is surely obtained; obtaining an equivalent visual region of an other ocular optical lens in accordance with a same method; and displaying the two equivalent visual regions on a same screen in a manner such that the regions can be compared. The equivalent visual region is a visual region obtained from the prism characteristics and the Abbe number at the point arbitrarily selected as described above and is different from the region of comfortable vision which was obtained in a manner such that the specific value of visual acuity is surely obtained at each point of the ocular optical lens. The arbitrarily selected point may be a single point or a plurality of points.
In a tenth preferred embodiment, the present invention provides a method for evaluating an ocular optical lens according to the ninth embodiment, wherein an image of actual vision at the selected point is created and the image of actual vision and the equivalent visual region are displayed on the same screen so that the image and the region can be compared.
In an eleventh preferred embodiment, the present invention provides an apparatus for evaluating an ocular optical lens which comprises: means of input for inputting data of an optical system including an Abbe number, a lens dioptric power and a value of visual acuity and a lens shape of the ocular optical lens; means of calculation for obtaining a region of comfortable vision in which the value of visual acuity can be surely obtained based on the data input via the means of input; and means of display for displaying the region of comfortable vision obtained by the means of calculation and the lens shape on the same screen so that the region and the lens shape can be compared.
In a twelfth preferred embodiment, the present invention provides an apparatus for evaluating an ocular optical lens according to the eleventh embodiment, wherein the region of comfortable vision is marked out with and contained in a circle whose center is placed at an optical center of the ocular optical lens and whose radius has a value h in a following range:
hxe2x89xa6kve/|D|
wherein the following are defined as:
k: a constant
ve: an Abbe number
D: a lens dioptric power.
In a thirteenth embodiment, the present invention provides an apparatus for evaluating an ocular optical lens according to the eleventh and twelfth embodiments, but also includes: an apparatus for measuring an Abbe number which is used for measuring the Abbe number of the ocular optical lens; a lens meter for measuring a lens dioptric power of the ocular optical lens; a frame tracer for obtaining a shape of a lens frame; means of external input for inputting data obtained by the measurements using the apparatus for measuring an Abbe number, the lens meter and the frame tracer into the means of calculation; and means of manual input for inputting desired data of an optical system including the Abbe number into the means of calculation.
In a fourteenth preferred embodiment, the present invention provides a memory medium readable by a computer and storing a program for operating a computer, the program comprising: means for entering and processing data of an optical system of an ocular optical lens; means for generating a region of comfortable vision in which a specific value of visual acuity is surely obtained based on the data of an optical system; and means for displaying the obtained region of comfortable vision.
In accordance with the embodiments of the present invention, differences in vision due to the difference in the Abbe number of a lens is expressed as the area of the region of comfortable vision in which a specific value of visual acuity can be surely obtained. Thus, the Abbe number or the difference in the Abbe number which has previously been difficult for laypeople to appreciate can easily be recognized.
Further objects, features and advantages of the present invention will become apparent from the Detailed Description of Preferred Embodiments, which follows, when considered together with the attached Drawings.